"Andrew Warbrick" wrote in message ...

What I was getting at is that the Microair is more
sensitive to a very slightly low battery voltage than
most glider instruments.

Radios in general are more sensitive to low voltage
than other glider instruments.


When I press the PTT the LX160
does not complain about low battery voltage which means
it's not going below 10V.


If you read your specs, the normal operating voltage is
listed as 13.8 volts, and "emergency minimum" is
listed at 10.5. Any radio you're likely to buy for a glider
has serious problems transmitting below 11 volts, either
distortion or total failure to transmit. If you are down at
10-11 volts, that certainly is not "very slightly" below
the rated voltage of the radio.


My main battery is a 12V 12Ah Yuasa, it was new in
March and has only been charged about a dozen times
with an appropriate battery charger. It is expected
to run an Ipaq (up to 2A more likely 0.5A) an LX160s,
the radio and from time to time an artificial horizon
(peak current 2A, 1.6A when running) it will run all
of this kit for up to eight hours (tested in flight).
This probably causes the battery voltage to fall to
round about 10.5-11V after about 3 hours use. This
is enough to upset the Microair.

You're making guesses about the battery voltage. You
don't really know what the battery voltage is, and you
don't really know about the losses in the other parts of the
electrical system. Measuring the voltage at the radio during
the failure to transmit is the only way to actually diagnose the
problem. Certainly can do that on the ground after a long
flight, or a simulated long flight.


The fin battery is
12V 7Ah made up of two 6V 7Ah Yuasa batteries, it also
was new in March but I keep it as a backup to ensure
I'm never without a horizon in the event of the main
battery going down, I've had to resort to using the
fin battery to power the radio because that's the only
way to get reliable transmission out of the Microair.

There could be two possible causes for this. The voltage
out of the main battery is down slightly under load
and the Microair doesen't like it. Or, another device
is putting electrical noise on the 12V line and the
Microair doesen't like that.

Or one of the cells in the main battery got damaged from
being dropped. Or you have defective wiring. Or you get
significant drops from diodes that people like to sprinkle into
multi-battery systems. Or one of your many switches has
bad contacts. Or you've got a slow-blow fuse with excessive
resistance. These are just a few of the possibilities. There
is absolutely no substitute for measuring the voltage, and then
studying the specs in your manual.


I'm not going to go for a 14V battery, strapping a
mismatched 2V cell to a 12V battery is a truly awful
solution to bady designed instruments that won't work
properly with a 12V battery.

Gosh, I've got 7 perfectly matched cells in a battery that
fits in the tail fin, powers the whole panel for 6 hours no
problem. I haven't seen less than 13.5 volts, during transmit,
at the end of long flights. Never has glitched the flight recorder,
and I don't have to be distracted with flipping switches during
the flight to try to find enough juice to keep things powered.
There is a certain elegance in using a proper battery in the first
place. Let's see, 14 volt radio, 14 volt battery. No wonder it
works so good.

Starting with a battery two volts too low, then slapping on
a DC-DC converter to try to compensate for undiagnosed
problems in your electrical system doesn't strike me as
an elegant solution.


We have similar problems with the Microair 760 fitted
to one of the club's Puchacz, if the battery voltage
is slightly low the radio won't transmit even though
the vario and turn and slip work fine.

That's just the way radios work, if you have an inadequate
electrical system. They're the first to fail due to low voltage.
Dittels and Beckers don't work at low voltage either.

Dave Kinsell